Wireless transmission apparatus and modulation scheme selection method

ABSTRACT

A wireless transmission apparatus that can accurately select an optimal modulation scheme on a per block basis in a multi-carrier communication system in which block division of subcarriers and adaptive modulation are performed. In this wireless transmission apparatus, a propagation path characteristics acquisition section ( 107 ) acquires the average SNR and SNR dispersion for each block, which are estimated by a wireless reception apparatus ( 200 ), using received signals inputted from a reception RF section ( 106 ) and outputs these to an assignment section ( 108 ), the assignment section ( 108 ) selects a modulation scheme for each block based on the average SNR and SNR dispersion of each block inputted from the propagation path characteristics acquisition section ( 107 ), and modulation sections ( 101 - 1, 101 - 2, . . . , 101 -L) modulate multi-carrier signals included in each block, with the modulation scheme for each block selected by the assignment section ( 108 ).

This is a continuation application of application Ser. No. 10/564,089filed Jan. 11, 2006, which is based on and claims priority of JP2003-284,509, the entire contents of which are incorporated by referencein their entirety.

TECHNICAL FIELD

The present invention relates to a wireless transmission apparatus and amodulation scheme selection method.

BACKGROUND ART

In a communication system in which adaptive modulation is performed, anoptimal modulation scheme is selected based on propagation pathcharacteristics that change with time. High-speed data communication canbe performed by selecting the fastest modulation scheme that can satisfythe desired error rate (e.g., Packet Error Rate: PER=1%) based onpropagation path characteristics. For example, when adaptive modulationis applied to downlink channels, the propagation path characteristicsmeasured by a mobile station at the data receiving end are reported to abase station at the data transmitting end, and then the base stationselects an optimal modulation scheme for the reported currentpropagation path characteristics and transmits data to the mobilestation.

In the communication system in which such adaptive modulation isperformed, the average signal to noise ratio (SNR) measured at the datareceiving end is most commonly used as the value representingpropagation path characteristics. Furthermore, in order to improve theaccuracy of modulation scheme selection, a method of selecting amodulation scheme is also proposed taking into account delay spread aswell as average SNR (for example, see H. Matsuoka, T. Ue, S. Sampei andN. Morinaga, “An Analysis on the Performance of Variable Symbol Rate andModulation Level Adaptive Modulation System”, TECHNICAL REPORT OF IEICE,RCS 94-64 (1994-09), pp. 31-36: hereinafter referred to as “reference1”). In addition, in multi-carrier communication system such asorthogonal frequency division multiplexing (OFDM) system, a method ofselecting a modulation scheme is also proposed based on average SNR andvariation in propagation path characteristics between adjacentsubcarriers (for example, see Unexamined Japanese Patent Publication No.2001-103032: hereinafter referred to as “reference 2”).

Now, when adaptive modulation is applied to a multi-carriercommunication system, adaptive modulation is implemented per subcarrier.Therefore, at the data receiving end, it is necessary to report to thedata transmitting end the value representing propagation pathcharacteristics per subcarrier.

For example, in a mobile communications system in which frequencyscheduling is performed such that the base station assigns to aplurality of mobile stations different subcarriers based on thepropagation path characteristics of the downlink channel of eachsubcarrier, all of the plurality of mobile stations report to the basestation the propagation path characteristics per subcarrier, and thevolume of traffic increase on uplink channels. In order to solve thisproblem, it has been proposed to divide a plurality of subcarriers isinto a number of blocks (i.e., block division of subcarriers) and carryour frequency scheduling on a per block basis. According to this method,since each mobile station has only to report propagation pathcharacteristics on a per block basis, the volume of traffic on uplinkchannels can be reduced considerably compared with the case wherepropagation path characteristics are reported on a per subcarrier basis.If adaptive modulation is applied to a communication system in whichsuch block division of subcarriers is carried out, all subcarriersbelonging to the same block are modulated with the same modulationscheme.

However, in the above-noted prior art examples, if adaptive modulationis performed in a communication system where block division ofsubcarriers is carried out, there is a problem that the optimalmodulation scheme cannot be accurately selected, for the followingreasons.

For instance, since the delay spread in above reference 1 representsvariations in propagation path characteristics over full bandwidth, itcannot represent the variation in narrowband propagation pathcharacteristics of each block, when subcarriers are divided into blocks.Consequently, when subcarriers are divided into blocks, the optimalmodulation scheme cannot be selected accurately.

One instance for estimating the variation in propagation pathcharacteristics between adjacent subcarriers as in the above reference 2based on SNR variation is shown in FIG. 8. Namely, in case a, the SNRvalue varies between 2 and 3 among four subcarriers in one block, and sothe normalized SNR error representing the SNR variation between adjacentsubcarriers is 0.3. On the other hand, in cases b and c, although thevariation of SNR values among four subcarriers in one block is greaterthan in case a, the normalized SNR error is 0.3, which is the same as incase a. In this way, when subcarriers are divided into blocks, thevariation in propagation path characteristics between adjacentsubcarriers (i.e. normalized SNR error) sometimes have the same valueboth in case a where SNR variation is relatively small and in cases band c where SNR variation is relatively large. Under such circumstances,the variation in propagation path characteristics with in each blockcannot be estimated accurately, and the optimal modulation scheme cannotbe selected accurately for cases a to c, when subcarriers are dividedinto blocks.

As mentioned above, when bock division of subcarriers is carried out, itis difficult to accurately select the optimal modulation by the methodof reference 1 or reference 2 in cases where subcarriers are dividedinto blocks. Therefore, to perform adaptive modulation in communicationsystems in which block division of subcarriers is carried out, it isnecessary to introduce new parameters that optimally representvariations in narrowband propagation path characteristics of each block.

DISCLOSURE OF INVENTION

It is therefore an object of the present invention to provide a wirelesstransmission apparatus and a modulation scheme selection method that canaccurately select the optimal modulation scheme on a per block basis ina multi-carrier communication system where block division of subcarriersand adaptive modulation are performed.

To achieve the above object, with the present invention, “dispersion”refers to values that represent variations in propagation pathcharacteristics of each block in a multi-carrier communication systemwhere block division of subcarriers and adaptive modulation areperformed.

A wireless transmission apparatus according to the present inventionperforms adaptive modulation with a multicarrier signal formed with aplurality of blocks, each block including a plurality of subcarriersignals, the wireless transmission apparatus comprising, and thiswireless transmission apparatus employs a configuration having: aselection section that selects modulation schemes of the plurality ofblocks on a per block basis; and a modulation section that modulates theplurality of subcarrier signals in the plurality of blocks using themodulation schemes selected on a per block basis, and the selectionsection selects the modulation schemes on a per block basis based on anaverage and a dispersion of values representing propagation pathcharacteristics of each block.

With this configuration, variations in propagation path characteristicsof each block are represented accurately by dispersion of valuesrepresenting propagation path characteristics, so that the optimalmodulation scheme can be accurately selected on a per block basis in amulti-carrier communication system in which block division ofsubcarriers and adaptive modulation are performed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of a wirelesstransmission apparatus and a wireless reception apparatus according toEmbodiment 1 of the present invention;

FIG. 2 is a block diagram showing a configuration of a propagation pathcharacteristics estimation section in the wireless reception apparatusaccording to Embodiment 1 of the present invention;

FIG. 3 is a diagram for explaining SNR dispersion determined by thepropagation path characteristics estimation section in the wirelessreception apparatus according to Embodiment 1 of the present invention;

FIG. 4 is a diagram for explaining modulation scheme selection(selection method 1) performed by an assignment section in the wirelesstransmission apparatus according to Embodiment 1 of the presentinvention;

FIG. 5 is a diagram for explaining modulation scheme selection(selection method 2) performed by an assignment section in the wirelesstransmission apparatus according to Embodiment 1 of the presentinvention;

FIG. 6 is a block diagram showing a configuration of a propagation pathcharacteristics estimation section in a wireless reception apparatusaccording to Embodiment 2 of the present invention;

FIG. 7 is a block diagram showing a configuration of a propagation pathcharacteristics estimation section in a wireless reception apparatusaccording to Embodiment 3 of the present invention; and

FIG. 8. is a diagram for explaining parameters representing conversionaldispersion of propagation path characteristics (normalized SNR errors).

BEST MODE FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be explained below indetail with reference to the accompanying drawings.

Embodiment 1

A case will be described with this embodiment where SNR dispersion isused as a value representing variations in propagation pathcharacteristics in each block.

FIG. 1 is a block diagram showing a configuration of a wirelesstransmission apparatus and a wireless reception apparatus according toEmbodiment 1 of the present invention.

In the following, an OFDM system will be used as a multi-carriercommunication system.

A wireless transmission apparatus 100 shown in FIG. 1 mainly comprises:modulation sections 101-1, 101-2, 101-L; inverse fast Fourier transform(IFFT) section 102; guard interval (GI) insertion section 103;transmission RF section 104; transmitting and receiving antenna 105;reception RF section 106, propagation path characteristics acquisitionsection 107; assignment section 108; and assignment result storagesection 109. This wireless transmission apparatus 100 is mounted, forexample, in a base station in an OFDM system.

Also, wireless reception apparatus 200 shown in FIG. 1 mainly comprises:transmitting and receiving antenna 201; reception RF section 202; guardinterval (GI) removal section 203, fast Fourier transform (FFT) section204; propagation path characteristics estimation section 205; equalizer206; demodulation sections 207-1, 207-2, . . . , 207-L; parallel/serialconversion (P/S) section 208; assignment information acquisition section209; and transmission RF section 210. This wireless reception apparatus200 is mounted, for example, in the mobile station of any of users 1 toK in the OFDM system.

The modulation sections 101-1, 101-2, . . . , 101-L modulate signals ofusers 1, 2, . . . , K inputted via the assignment result storage section109, applying different modulation schemes (64QAM, 16QAM, QPSK, andBPSK) to each of blocks 1-L based on the block assignment results ofusers 1 to K stored in the assignment result storage section 109 andmodulation scheme information inputted from the assignment section 108.Also, the modulation scheme of each block is selected by the assignmentsection 108, according to the propagation path characteristics of eachblock estimated by the wireless reception apparatus 200. Here, thenumber of subcarriers contained in one OFDM signal is N, and these Nsubcarriers are divided into L blocks in increments of S subcarriers.Therefore, the number of blocks L is given by: L=N/S. Then allsubcarrier signals 1-S belonging to each block are modulated with thesame modulation scheme on a per block basis. For example, the modulationsection 101-1 modulates all subcarrier signals belonging to block 1 with64QAM when the propagation path characteristics for block 1 areestimated to be good, and modulates all subcarrier signals belonging toblock 1 with BPSK when the propagation path characteristics for block 1are estimated to be poor. When the propagation path characteristics forblock 1 are estimated to be extremely poor, the wireless transmissionapparatus 100 may not transmit all subcarrier signals belonging to block1. The signals modulated in this way are outputted to the IFFT section102.

The IFFT section 102 performs an inverse fast Fourier transform witheach modulated signal inputted from the modulation sections 101-1-101-Lto generate an OFDM signal (time waveform signal), and outputs the OFDMsignal to the GI insertion section 103.

The GI insertion section 103 inserts a guard interval for improvingdelay characteristics in the OFDM signal inputted from the IFFT section102, and outputs the result to the transmission RF section 104.

The transmission RF section 104 up-converts the OFDM signal inputtedfrom the GI insertion section 103 to RF band, and transmits it to thewireless reception apparatuses 200 of users 1 to K from the transmittingand receiving antenna 105.

The reception RF section 106 receives signals transmitted from thewireless reception apparatuses 200 of users 1 to K, from thetransmitting and receiving antenna 105, down-converts these signals fromRF band, and output the results to the propagation path characteristicsacquisition section 107.

The propagation path characteristics acquisition section 107 acquiresthe propagation path characteristics information with respect to eachblock estimated by the wireless reception apparatuses 200 of users 1 toK, from the received signals inputted from the reception RF section 106,and outputs them to the assignment section 108.

The assignment section 108 assigns blocks to users 1 to K and selects amodulation scheme on a per block basis, based on the propagation pathcharacteristics information with respect to each block inputted from thepropagation path characteristics acquisition section 107, stores theblock assignment results in the assignment result storage section 109,and outputs modulation scheme information representing the selectedmodulation schemes to the modulation sections 101-1, 101-2, . . . ,101-L. The assignment section 108 may perform the block assignment andmodulation scheme selection, taking into consideration also QoS (Qualityof Service: for example, each user's required data transmission rateand/or required error rate) set for each of users 1 to K.

The assignment result storage section 109 stores the block assignmentresults for users 1 to K inputted from the assignment section 108.

In addition, information that indicates which block is modulated withwhich modulation scheme and which user's signal is assigned to whichblock of subcarriers (modulation scheme assignment information) isincluded in the OFDM signal and the OFDM signal is transmitted to thewireless reception apparatus 200.

Next, the configuration of the wireless reception apparatus 200 will beexplained. Now, in the following explanation, the wireless receptionapparatus will assumed to be that of user 1 of users 1 to K.

The reception RF section 202 receives the OFDM signal via thetransmitting and receiving antenna 201, and outputs the OFDM signal tothe GI removal section 203 and the assignment information acquisitionsection 209.

The GI removal section 203 removes the guard interval from the OFDMsignal inputted from the reception RF section 202, and outputs the OFDMsignal to the FFT section 204.

The FFT section 204 carries out the fast Fourier transform (FFT) of theOFDM signal after the guard interval removal inputted from the GIremoval section 203 and transforms the OFDM signal to a signal of thefrequency domain from a signal of the time domain. By this FFT, signalstransmitted by a plurality of subcarriers are taken out and outputted tothe equalizer 206 and the propagation path characteristics estimationsection 205.

The propagation path characteristics estimation section 205 estimatesthe propagation path characteristics of each signal inputted from theFFT section 204, and outputs information (propagation pathcharacteristics information) representing the propagation pathcharacteristics to the equalizer 206 and the transmission RF section210. More specifically, the propagation path characteristics estimationsection 205 outputs the information representing the propagation pathcharacteristics estimated per subcarrier to the equalizer 206, andoutputs information representing the average and the dispersion in thepropagation path characteristics estimated per block to the transmissionRF section 210.

The equalizer 206 corrects the amplitude and phase distortion componentsin each signal inputted from the FFT section 204, based on thepropagation path characteristics information inputted from thepropagation path characteristics estimation section 205, and outputs thecorrected signal to the demodulation sections 207-1, 207-2, . . . ,207-L.

The demodulation sections 207-1, 207-2, . . . , 207-L have demodulationfunctions corresponding respectively to modulation sections 101-1,101-2, . . . , 101-L, and determine the demodulation scheme for eachblock based on the modulation scheme assignment information inputtedfrom the assignment information acquisition section 209, demodulate thesignals inputted from the equalizer 206 on a per block basis, and outputthe data after the demodulation to the P/S section 208 in parallel. Atthis time, the demodulation sections 207-1, 207-2, . . . , 207-Ldemodulate only the blocks including subcarrier signals for user 1 basedon the modulation scheme assignment information.

The P/S section 208 converts the parallel data inputted from thedemodulation sections 207-1, 207-2, . . . , 207-L into serial data, andthen outputs the data as user 1's desired received data.

The assignment information acquisition section 209 acquires themodulation scheme assignment information from the OFDM signal inputtedfrom the reception RF section 202, and outputs the information to thedemodulation sections 207-1, 207-2, . . . , 207-L.

The transmission RF section 210 transmits the propagation pathcharacteristics information inputted from the propagation pathcharacteristics estimation section 205 to the wireless transmissionapparatus 100 from the transmitting and receiving antenna 201.

Next, the propagation path characteristics estimation section 205 in thewireless reception apparatus 200 having the above-describedconfiguration will be explained. FIG. 2 is a block diagram showing aconfiguration of the propagation path characteristics estimation section205.

A block extraction section 2051 extracts the subcarrier signals inputtedfrom the FFT section 204 per block 1 to L, and outputs the signals to apilot extraction section 2052.

Of the data and pilot assigned to each subcarrier, the pilot extractionsection 2052 extracts only the pilot portion alone per block 1 to L, andoutputs the pilot portion to an SNR estimation section 2053.

The SNR estimation section 2053 estimates the SNR (instantaneous SNR)each of pilot portion per block 1 to L, and outputs the results to a SNRaverage calculation section 2054 and a SNR dispersion calculationsection 2055. The SNR estimation section 2053 estimates theinstantaneous SNR as follows.

First, the SNR estimation section 2053 calculates the channel estimationvalue: h, according to Equation (1). In Equation (1), h_(l)(s,i) is thechannel estimation value corresponding to the ith pilot portion on thetime-axis of the sth subcarrier in the lth block, and y_(l)(s,i) andd_(l)(s,i) is the received signal and the corresponding known pilotsymbol of the ith pilot portion on the time-axis of the sth subcarrierin the lth block, respectively. In addition, “*” is the complexconjugate. $\begin{matrix}{{h_{l}\left( {s,i} \right)} = {\frac{y_{l}\left( {s,i} \right)}{d_{l}\left( {s,i} \right)} = \frac{{y_{l}\left( {s,i} \right)} \cdot {d_{l}^{*}\left( {s,i} \right)}}{{{d_{l}\left( {s,i} \right)}}^{2}}}} & (1)\end{matrix}$

where l is l=1, 2, . . . , N/S, and s=1, 2, . . . , S;

N is the total number of all subcarriers in the received OFDM signal;and

S is the number of subcarriers contained in a one block.

Next, instantaneous SNR: g is calculated according to Equation (2). InEquation (2), g_(l)(s,i) is the instantaneous SNR corresponding to theith pilot portion on the time-axis of the sth subcarrier in the lthblock, P₀ is the transmitted signal power for each subcarrier, and N₀ isthe noise power for each subcarrier. $\begin{matrix}{{g_{l}\left( {s,i} \right)} = {\frac{P_{0}}{N_{0}}{h_{l}\left( {s,i} \right)}}} & (2)\end{matrix}$

The SNR average calculation section 2054 averages a plurality ofinstantaneous SNRs per block 1 to L according to Equation (3), determinethe average SNR (SNRm_(l)), and outputs these average SNR to the SNRdispersion calculation section 2055. Also, the SNR average calculationsection 2054 outputs the average SNR (SNRm_(l)) as propagation pathcharacteristics information to the transmission RF section 210. Here,SNRm_(l) is the average SNR of the lth block, and I is the number ofpilot symbols in each subcarrier on the time-axis. $\begin{matrix}{{SNRm}_{l} = {\frac{1}{SI}{\sum\limits_{s = 1}^{S}{\sum\limits_{i = 1}^{I}{g_{i}\left( {s,i} \right)}}}}} & (3)\end{matrix}$

SNR dispersion calculation section 2055 calculates SNR dispersion:SNRv_(l) per block 1 to L, according to Equation (4), and outputsSNRv_(l) as propagation path characteristics information, to thetransmission RF section 210. Here, SNRv_(l) is SNR dispersion with thelth block. $\begin{matrix}{{SNRv}_{l} = {\frac{1}{SI}{\sum\limits_{s = 1}^{S}{\sum\limits_{i = 1}^{I}\left( {{g_{l}\left( {s,i} \right)} - {SNR}_{m}} \right)^{2}}}}} & (4)\end{matrix}$

Here, FIG. 3 shows the SNR dispersion calculated according to Equation(4) in the same cases a through c as shown in FIG. 8 mentioned above.For example, in case a, S=4 (the number of subcarriers contained in oneblock), I=1 (assuming that one pilot symbol is assigned to eachsubcarrier), and g=2, 3, 2, 3 (the instantaneous SNR of thesubcarriers), and Equations (3) and (4) give SNRm (average SNR)=2.5 andSNRv (SNR dispersion)=0.25. Similarly, in case b and case c, Equations(3) and (4) give SNRm (average SNR)=2.5 and SNRv (SNR dispersion)=1.25,respectively. That is, in case a where SNR variation is relativelysmall, the SNR dispersion is small, while in case b and case c where SNRvariation is relatively large, the SNR dispersion is large. From thisresult, it is understood that the variation in propagation pathcharacteristics in each block can be estimated accurately by using SNRdispersion as a parameter for estimating the variation in propagationpath characteristics in each block. Therefore, at the wirelesstransmission apparatus 100, the optimal modulation scheme to each ofcases a through c can be selected accurately, when block division ofsubcarriers is carried out.

Next, the modulation scheme selection performed by the assignmentsection 108 in the wireless transmission apparatus 100 having theabove-described configuration will be explained. Here, one modulationscheme is selected from 64QAM, 16QAM, QPSK and BPSK according to thefollowing selection method 1 or 2.

<Selection Method 1>

The assignment section 108 selects the modulation scheme of the besttransmission efficiency, based on the propagation path characteristicsinformation, i.e. SNRm, (average SNR) and SNRv (SNR dispersion),inputted from the propagation path characteristics acquisition section107. The correspondence among SNRm (average SNR), SNRv (SNR dispersion)and modulation scheme at predetermined PER (for example, PER=10⁻¹) isshown in FIG. 4. In FIG. 4, a given 2-dimensional coordinate space isdivided in advance by reciprocal function of SNR dispersion and averageSNR in five areas, and a modulation scheme (including “no transmission”)is assigned to each area. So, the estimated propagation pathcharacteristics are represented by coordinates (SNRm, 1/SNRv), and themodulation scheme and the coding rate corresponding to the area in whichthe coordinates are located are selected.

<Selection Method 2>

As weighted (weighted in dB value) SNR, the following four are defined.SNRw1=SNRm−sqrt(SNRv)*w  (1)SNRw2=SNRm−sqrt(SNRv)*w(|SNR _(max) −SNRm|/|SNRm _(max)|)  (2)SNRw3=SNRm−sqrt(SNRv)*w(fd/fd _(max))  (3)SNRw4=SNRm−sqrt(SNRv)*w(σ/σ_(max))  (4)

Here, SNRm_(max), fd_(max), and σ_(max) are the maximum average SNR, themaximum possible Doppler frequency, and the maximum possible delayspread, respectively. Sqrt(SNRv) represents the square root of SNRv. Inaddition, weighting factor w is a constant for SNRw1, a function of thenormalized average SNR for SNRw2, a function of the normalized Dopplerfrequency fd for SNRw3, and a function of the normalized delay spreadfor SNRw4. For example, weighting factor w takes values given byEquation (5). $\begin{matrix}{{w(x)} = \left\{ \begin{matrix}{x^{2},} & {0 \leq x \leq 1} \\{1,} & {x > 1}\end{matrix} \right.} & (5)\end{matrix}$

Then, the modulation scheme and the coding rate are selected as followsfrom the PER-SNR static characteristics as shown in FIG. 5. First, usingthe static characteristics shown in FIG. 5, the threshold value (T1-T4)for each modulation scheme is determined in correspondence with therequired PER (10⁻¹ in FIG. 5). Next, SNRw3 is calculated for a specificDoppler frequency fd. If SNRw3>=T4, 64QAM (coding rate R=½); ifT3<=SNRw3<T4, 16QAM (R=½); if T2<=SNRw3<T3, QPSK (R=½); and ifT1<=SNRw3<T2, BPSK (R=½) is selected.

Alternatively, SNRw4 may be calculated for a specific delay spread σ. IfSNRw4>=T4, 64QAM (R=½); if T3<=SNRw4<T4, 16QAM (R=½); if T2<=SNRw4<T3,QPSK (R=½); and if T1<=SNRw4<T2, BPSK (R=½) is selected. Alternatively,for SNRw1 and SNRw2, the modulation scheme and the coding rate may beselected from the PER-SNR characteristics shown in FIG. 5, as with SNRw3and SNRw4.

In this way, with this embodiment, SNR dispersion is used as a parameterrepresenting the variation in propagation path characteristics in eachblock in the communication system in which block division of subcarriersis carried out, so that the variation in propagation pathcharacteristics in each block can be estimated accurately, and, as aresult, the optimal modulation scheme can be accurately selected inadaptive modulation.

Additionally, although with this embodiment, the SNR dispersion is usedas a parameter representing the variation in propagation pathcharacteristics in each block, the following parameters can be obtainedby modifying the Equation (4) defining SNR dispersion. Each parametercan be used as a parameter representing the variation in propagationpath characteristics in each block, just as SNR dispersion.

Average change amount of instantaneous SNR$u_{l} = {\frac{1}{SI}{\sum\limits_{s = 1}^{S}{\sum\limits_{i = 1}^{I}{{{g_{l}\left( {s,i} \right)} - {SNRm}_{l}}}}}}$

Maximum change amount of instantaneous SNR$v_{l} = {\max\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{{{g_{l}\left( {s,i} \right)} - {SNRm}_{l}}}}$

Square of maximum change amount of instantaneous SNR$x_{l} = {\max\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{{{g_{l}\left( {s,i} \right)} - {SNRm}_{l}}}^{2}}$

Difference between maximum and minimum of instantaneous SNR$z_{l} = {\frac{1}{2}{{{\max\quad{\underset{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{g_{l}}\left( {s,i} \right)}} - {\min\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{g_{l}\left( {s,i} \right)}}}}}$

Difference between square of maximum and square of minimum ofinstantaneous SNR$d_{l} = {{\max\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{{g_{l}\left( {s,i} \right)}}^{2}} - {\min\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{{g_{l}\left( {s,i} \right)}}^{2}}}$

Embodiment 2

In this embodiment, the case where dispersion of channel estimationvalue is used as a value representing the variations of the propagationpath characteristics in each block is explained.

FIG. 6 is a block diagram showing a configuration of a propagation pathcharacteristics estimation section 205 according to Embodiment 2 of thepresent invention. In FIG. 6, the same portions as in FIG. 2 (inEmbodiment 1) will be assigned the same reference numerals as in FIG. 2to omit detailed explanations thereof.

The channel estimation value calculation section 2056 calculates channelestimation values from above Equation (1), and outputs these values to achannel dispersion calculation section 2057.

The channel dispersion calculation section 2057 calculates thedispersion of channel estimation values: Hv_(l) per block 1 to L fromEquation (6), and outputs the result to the transmission RF section 210as propagation path characteristics information. Now, Hv_(l) representsthe dispersion of the channel estimation value of the lth block. Here,Equation (6) is derived, assuming that in Equation (2) mentioned above,P₀ and N₀ are constants for all subcarriers in a block. $\begin{matrix}{{{Hv}_{l} = {\frac{1}{SI}{\sum\limits_{s = 1}^{S}{\sum\limits_{i = 1}^{I}\left( {{h_{l}\left( {s,i} \right)} - {Hm}_{l}} \right)}}}}{{where},{{Hm}_{l} = {\frac{1}{SI}{\sum\limits_{s = 1}^{S}{\sum\limits_{i = 1}^{I}{h_{l}\left( {s,i} \right)}}}}}}} & (6)\end{matrix}$

By using this channel estimation value dispersion as a parameter forestimating the variation in propagation path characteristics in eachblock, the variation in propagation path characteristics in each blockcan be estimated accurately as with Embodiment 1. Therefore, accordingto this embodiment, the optimal modulation scheme can be accuratelyselected, when adaptive modulation is performed in the communicationsystem in which block division of subcarriers is carried out.

Also by using the dispersion of channel estimation value as a parameterfor estimating the variation in the propagation path characteristics ineach block, wireless transmission apparatus 100 can select modulationscheme with the same selection method as in Embodiment 1. In selectionmethod 2, as weighted SNR, the following four are defined:SNRw1=SNRm−Hv*w  (1)SNRw2=SNRm−Hv*w(|Hv _(max) −Hv|/|Hv _(max)|)  (2)SNRw3=SNRm−Hv*w(fd/fd _(max))  (3)SNRw4=SNRm−Hv*w(σ/σ_(max))  (4)

Additionally, with this embodiment, the dispersion of channel estimationvalues is used as a parameter representing the variation in thepropagation path characteristics in each block, the following parameterscan be obtained by modifying the Equation (6) defining the dispersion ofchannel estimation values. Each parameter can be used as a parameterrepresenting the variation in the propagation path characteristics ineach block, just as the dispersion of channel estimation values.

Average change amount of channel estimation values$u_{l} = {\frac{1}{SI}{\sum\limits_{s = 1}^{S}{\sum\limits_{i = 1}^{I}{{{h_{l}\left( {s,i} \right)} - {Hm}_{l}}}}}}$

Maximum change amount of channel estimation values$v_{l} = {\max\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{{{h_{l}\left( {s,i} \right)} - {Hm}_{l}}}}$

Square of maximum change amount of channel estimation values$x_{l} = {\max\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{{{h_{l}\left( {s,i} \right)} - {Hm}_{l}}}^{2}}$

Difference between maximum and minimum of channel estimation values$z_{l} = {\frac{1}{2}{{{\max\quad{\underset{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{h_{l}}\left( {s,i} \right)}} - {\min\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{h_{l}\left( {s,i} \right)}}}}}$

Difference between square of maximum and square of minimum of channelestimation values$d_{l} = {{\max\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{{h_{l}\left( {s,i} \right)}}^{2}} - {\min\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{{h_{l}\left( {s,i} \right)}}^{2}}}$

Embodiment 3

A case will be described below with this embodiment where dispersion ofamplitude values of signals of pilot portions (pilot dispersion) is usedas a value representing the variation in propagation pathcharacteristics of each block.

FIG. 7 is a block diagram showing a configuration of a propagation pathcharacteristics estimation section 205 according to Embodiment 3 of thepresent invention. In FIG. 7, the same portions as in FIG. 2 (inEmbodiment 1) will be assigned the same reference numerals as in FIG. 2to omit detailed explanations thereof.

A pilot dispersion calculation section 2058 calculates pilot dispersionYv_(l) per block 1 to L from Equation (7), and outputs Yv_(l) to thetransmission RF section 210, as propagation path characteristicsinformation. Now, Yv_(l) represents the pilot dispersion of the lthblock. Here, Equation (7) is derived, considering that in Equation (1)mentioned above, the denominator is a constant. $\begin{matrix}{{{Yv}_{l} = {\frac{1}{SI}{\sum\limits_{s = 1}^{S}{\sum\limits_{i = 1}^{I}\left( {{y_{l}\left( {s,i} \right)} - {Ym}_{l}} \right)^{2}}}}}{{where},{{Ym}_{l} = {\frac{1}{SI}{\sum\limits_{s = 1}^{S}{\sum\limits_{i = 1}^{I}{y_{l}\left( {s,i} \right)}}}}}}} & (7)\end{matrix}$

By using this pilot dispersion as a parameter for estimating thevariation in the propagation path characteristics in each block, thevariation in the propagation path characteristics in each block can beestimated accurately, as with Embodiment 1. Therefore, with thisembodiment, the optimal modulation scheme can be accurately selected,when adaptive modulation is performed in the communication system inwhich block division of subcarriers is carried out.

Also by using the pilot dispersion as a parameter which estimates thevariations of the propagation path characteristics in each block,wireless transmission apparatus 100 can select modulation scheme withthe same selection method as in Embodiment 1. In selection method 2 asweighted SNR, the same four defined in Embodiment 2 will be definedagain in this embodiment. Additionally, although in the above-mentionedexamples, the pilot dispersion has been used as a parameter representingthe variation in the propagation path characteristics in each block, thefollowing parameters can be obtained by modifying the Equation (7)defining the pilot dispersion. Each of these can be used as a parameterrepresenting the variations of the propagation path characteristics ineach block, just as the pilot dispersion.

Average change amount of received signal of pilot portion$u_{l} = {\frac{1}{SI}{\sum\limits_{s = 1}^{S}{\sum\limits_{i = 1}^{I}{{{y_{l}\left( {s,i} \right)} - {Ym}_{l}}}}}}$

Maximum change amount of received signal of pilot portion$v_{l} = {\max\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{{{y_{l}\left( {s,i} \right)} - {Ym}_{l}}}}$

Square of maximum change amount of received signal of pilot portion$x_{l} = {\max\limits_{\underset{1 \leq s \leq S}{1 \leq i \leq I}}{{{y_{l}\left( {s,i} \right)} - {Ym}_{l}}}^{2}}$

Difference between maximum and minimum of received signal of pilotportion$z_{l} = {\frac{1}{2}{{{\max\limits_{\underset{\quad{1\quad \leq \quad s\quad \leq \quad S}}{1\quad \leq \quad i\quad \leq \quad I}}\quad{y_{l}\left( {s,i} \right)}} - {\min\limits_{\underset{\quad{1\quad \leq \quad s\quad \leq \quad S}}{1\quad \leq \quad i\quad \leq \quad I}}\quad{y_{l}\left( {s,i} \right)}}}}}$

Difference between square of maximum and square of minimum of receivedsignal of pilot portion$d_{l} = {{\max\limits_{\underset{\quad{1\quad \leq \quad s\quad \leq \quad S}}{1\quad \leq \quad i\quad \leq \quad I}}{{y_{l}\left( {s,i} \right)}}^{2}} - {\min\limits_{\underset{\quad{1\quad \leq \quad s\quad \leq \quad S}}{1\quad \leq \quad i\quad \leq \quad I}}{{y_{l}\left( {s,i} \right)}}^{2}}}$

Embodiment 4

When adaptive modulation is applied to the communication system in whichdividing of subcarriers into blocks is carried out, subcarriers whoseinstantaneous SNR is lower than or equal to the average SNR, among thesubcarriers of each block, mainly causes deterioration of thecommunication quality in each block. So, in this embodiment, dispersionis determined using only instantaneous SNRs less than or equal to theaverage SNR, in Embodiments 1 through 3.

Specifically, although with Embodiment 1 dispersion was calculated fromEquation (4) using S×I instantaneous SNRs, with this embodiment, SNRdispersion: SNRv_(l)′ is calculated from Equation (8) using only G_(S)instantaneous SNR lower than or equal to the average SNR. Now, G_(S)indicates the number of instantaneous SNRs having values less than orequal to the average SNR among S×I instantaneous SNRs. $\begin{matrix}{{{SNR}\quad v_{l}^{\prime}} = {\frac{1}{G_{S}}\underset{{g_{\quad l}{({s,i})}} < {SNRm}_{\quad l}}{\sum\limits_{s = 1}^{S}\sum\limits_{i = 1}^{I}}\left( {{g_{l}\left( {s,i} \right)} - {{SNR}\quad m_{l}}} \right)^{2}}} & (8)\end{matrix}$

Similarly, dispersion of channel estimation values: Hv_(l)′ iscalculated from Equation (9) using only G_(H) channel estimation valueslower than or equal to Hm_(l), instead of calculating dispersion ofchannel estimation values from Equation (6) in the above-mentionedEmbodiment 2. Now, G_(H) indicates the number of channel estimationvalues falling lower than or equal to the average channel estimationvalue among S×I channel estimation values. $\begin{matrix}{{H\quad v_{l}^{\prime}} = {\frac{1}{G_{H}}\underset{{h_{\quad l}{({s,i})}} < {H\quad m_{\quad l}}}{\sum\limits_{s = 1}^{S}\sum\limits_{i = 1}^{I}}\left( {{h_{l}\left( {s,i} \right)} - {H\quad m_{l}}} \right)^{2}}} & (9)\end{matrix}$

Similarly, although with Embodiment 3 pilot dispersion was calculatedfrom equation (7), with this embodiment, pilot dispersion: Yv_(l)′ iscalculated from Equation (10) using only G_(Y) received signals of pilotportions with amplitudes smaller than or equal to Ym_(l). Now, G_(Y)indicates the number of received signals of pilot portions less than orequal to the average amplitude among S×I received signals of pilotportions. $\begin{matrix}{{Y\quad v_{l}^{\prime}} = {\frac{1}{G_{Y}}\underset{{y_{\quad l}{({s,i})}} < {Y\quad m_{\quad l}}}{\sum\limits_{s = 1}^{S}\sum\limits_{i = 1}^{I}}\left( {{y_{l}\left( {s,i} \right)} - {Y\quad m_{l}}} \right)^{2}}} & (10)\end{matrix}$

Thus, according to this embodiment, since the dispersion in propagationpath characteristics is obtained using only subcarriers causingdeterioration in communication quality of block among all subcarriers ineach block, the optimal modulation scheme can be selected moreaccurately, when adaptive modulation is performed in the communicationsystem in which block division of subcarriers is carried out.

Furthermore, in this embodiment, the following parameters can also becited in addition to the parameters cited as the parameters indicatingthe variation of the propagation path characteristic in each block thatare capable of being used with dispersions in Embodiments 1 through 3.

Average change amount of instantaneous SNRs below average SNR$u_{l}^{\prime} = {\frac{1}{G_{S}}\underset{{g_{\quad l}{({s,i})}} < {{SNR}\quad m_{\quad l}}}{\sum\limits_{s = 1}^{S}\sum\limits_{i = 1}^{I}}{{{g_{l}\left( {s,i} \right)} - {{SNR}\quad m_{l}}}}}$

Maximum change amount of instantaneous SNRs below average SNR$v_{l}^{\prime} = {\underset{{g_{\quad l}{({s,i})}} < {{SNR}\quad m_{\quad l}}}{\max\limits_{\underset{\quad{1\quad \leq \quad s\quad \leq \quad S}}{1\quad \leq \quad i\quad \leq \quad I}}}{{{g_{l}\left( {s,i} \right)} - {{SNR}\quad m_{l}}}}}$

Square of maximum amount of instantaneous SNRs below average SNR$x_{l}^{\prime} = {\underset{{g_{\quad l}{({s,i})}} < {{SNR}\quad m_{\quad l}}}{\max\limits_{\underset{\quad{1\quad \leq \quad s\quad \leq \quad S}}{1\quad \leq \quad i\quad \leq \quad I}}}{{{g_{l}\left( {s,i} \right)} - {{SNR}\quad m_{l}}}}^{2}}$

Difference between maximum and minimum of instantaneous SNRs belowaverage SNR$z_{l}^{\prime} = {\frac{1}{2}{{{\underset{{g_{\quad l}{({s,i})}} < {{SNR}\quad m_{\quad l}}}{\max\limits_{\underset{\quad{1\quad \leq \quad s\quad \leq \quad S}}{1\quad \leq \quad i\quad \leq \quad I}}}\quad{g_{l}\left( {s,i} \right)}} - {\underset{{g_{\quad l}{({s,i})}} < {{SNR}\quad m_{\quad l}}}{\min\limits_{\underset{\quad{1\quad \leq \quad s\quad \leq \quad S}}{1\quad \leq \quad i\quad \leq \quad I}}}\quad{g_{l}\left( {s,i} \right)}}}}}$

Difference between square of maximum and square of minimum ofinstantaneous SNRs below average SNR$d_{l}^{\prime} = {{\underset{{g_{\quad l}{({s,i})}} < {{SNR}\quad m_{\quad l}}}{\max\limits_{\underset{\quad{1\quad \leq \quad s\quad \leq \quad S}}{1\quad \leq \quad i\quad \leq \quad I}}}{{g_{l}\left( {s,i} \right)}}^{2}} - {\underset{{g_{\quad l}{({s,i})}} < {{SNR}\quad m_{\quad l}}}{\min\limits_{\underset{\quad{1\quad \leq \quad s\quad \leq \quad S}}{1\quad \leq \quad i\quad \leq \quad I}}}{{g_{l}\left( {s,i} \right)}}^{2}}}$

Average change amount of channel estimation values below average value$u_{l}^{\prime} = {\frac{1}{G_{S}}\underset{{h_{l}{({s,i})}} < {H\quad m_{l}}}{\sum\limits_{s = 1}^{S}\sum\limits_{i = 1}^{I}}{{{h_{l}\left( {s,i} \right)} - {H\quad m_{l}}}}}$

Maximum change amount of channel estimation values below average value$v_{l}^{\prime} = {\underset{{h_{l}{({s,i})}} < {H\quad m_{l}}}{\underset{1 \leq s \leq S}{\max\limits_{1 \leq i \leq I}}}{{{h_{l}\left( {s,i} \right)} - {H\quad m_{l}}}}}$

Square of maximum amount of channel estimation values below averagevalue$x_{l}^{\prime} = {\underset{{h_{l}{({s,i})}} < {H\quad m_{l}}}{\underset{1 \leq s \leq S}{\max\limits_{1 \leq i \leq I}}}{{{h_{l}\left( {s,i} \right)} - {H\quad m_{l}}}}^{2}}$

Difference between maximum and minimum of channel estimation valuesbelow average value$z_{l}^{\prime} = {\frac{1}{2}{{{\underset{{h_{l}{({s,i})}} < {H\quad m_{l}}}{\underset{1 \leq s \leq S}{\max\limits_{1 \leq i \leq I}}}{h_{l}\left( {s,i} \right)}} - {\underset{{h_{l}{({s,i})}} < {H\quad m_{l}}}{\underset{1 \leq s \leq S}{\min\limits_{1 \leq i \leq I}}}{h_{l}\left( {s,i} \right)}}}}}$

Difference between square of maximum and square of minimum of channelestimation values below average value$d_{l}^{\prime} = {{\underset{{h_{l}{({s,i})}} < {H\quad m_{l}}}{\underset{1 \leq s \leq S}{\max\limits_{1 \leq i \leq I}}}{{h_{l}\left( {s,i} \right)}}^{2}} - {\underset{{h_{l}{({s,i})}} < {H\quad m_{l}}}{\underset{1 \leq s \leq S}{\min\limits_{1 \leq i \leq I}}}{{h_{l}\left( {s,i} \right)}}^{2}}}$

Average change amount of received signals of pilot portion below averageamplitude$u_{l}^{\prime} = {\frac{1}{G_{S}}\underset{{h_{l}{({s,i})}} < {Y\quad m_{l}}}{\sum\limits_{s = 1}^{S}\sum\limits_{i = 1}^{I}}{{{y_{l}\left( {s,i} \right)} - {Y\quad m_{l}}}}}$

Maximum change amount of received signals of pilot portion below averageamplitude$v_{l}^{\prime} = {\underset{{y_{l}{({s,i})}} < {Y\quad m_{l}}}{\underset{1 \leq s \leq S}{\max\limits_{1 \leq i \leq I}}}{{{y_{l}\left( {s,i} \right)} - {Y\quad m_{l}}}}}$

Square of maximum change amount of received signals of pilot portionbelow average amplitude$x_{l}^{\prime} = {\underset{{y_{l}{({s,i})}} < {Y\quad m_{l}}}{\underset{1 \leq s \leq S}{\max\limits_{1 \leq i \leq I}}}{{{y_{l}\left( {s,i} \right)} - {Y\quad m_{l}}}}^{2}}$

Difference between maximum and minimum of received signals of pilotportion below average amplitude$z_{l}^{\prime} = {\frac{1}{2}{{{\underset{{y_{l}{({s,i})}} < {Y\quad m_{l}}}{\underset{1 \leq s \leq S}{\max\limits_{1 \leq i \leq I}}}{y_{l}\left( {s,i} \right)}} - {\underset{{y_{l}{({s,i})}} < {Y\quad m_{l}}}{\underset{1 \leq s \leq S}{\min\limits_{1 \leq i \leq I}}}{y_{l}\left( {s,i} \right)}}}}}$

Difference between square of maximum and square of minimum of receivedsignals of pilot portion below average amplitude$d_{l}^{\prime} = {{\underset{{y_{l}{({s,i})}} < {Y\quad m_{l}}}{\underset{1 \leq s \leq S}{\max\limits_{1 \leq i \leq I}}}{{y_{l}\left( {s,i} \right)}}^{2}} - {\underset{{y_{l}{({s,i})}} < {Y\quad m_{l}}}{\underset{1 \leq s \leq S}{\min\limits_{1 \leq i \leq I}}}{{y_{l}\left( {s,i} \right)}}^{2}}}$

The functional blocks used above for explanation of the embodiments aretypically implemented as LSI, a type of integrated circuit. These blocksmay be each discretely integrated into one chip, or may be part of allintegrated into one chip.

Although LSI is mentioned here, the integrated chip may be an IC, SystemLSI, Super LSI, or Ultra LSI, depending on the degree of integration.

Moreover, the integration may be realized not only as LSI, but also asdedicated circuit or general-purpose processor. Field programmable gatearray (FPGA) which is programmable after LSI manufacture, orreconfigurable processor which is reconfigurable its connections andsetups of circuit cells inside LSI may be used.

Furthermore, as a result of the development of the semiconductortechnology and/or the derived technology, if a new technology ofintegration replacing LSI technology emerges the functional blocks maybe integrated using such new technology. Adaptation of biotechnologyetc. and so forth may be a possibility.

As explained above, according to the present invention, in themulti-carrier communication system in which block division ofsubcarriers and adaptive modulation are performed, the optimalmodulation scheme can be accurately selected on a per block basis, andas a result, transmission efficiency can be improved.

This application is based on Japanese Patent Application No. 2003-284509filed on Jul. 31, 2003, the entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use with mobile stationapparatuses and base station apparatuses and so forth used in mobilecommunications systems.

FIG. 1

-   101: MODULATION SECTION-   102: IFFT SECTION-   103: GI INSERTION SECTION-   104: TRANSMISSION RF SECTION-   106: RECEPTION RF SECTION-   107: PROPAGATION PATH CHARACTERISTICS ACQUISITION SECTION-   108: ASSIGNMENT SECTION-   109: ASSIGNMENT RESULT STORAGE SECTION-   202: RECEPTION RF SECTION-   203: GI REMOVAL SECTION-   204: FFT SECTION-   205: PROPAGATION PATH CHARACTERISTICS ESTIMATION SECTION-   206: EQUALIZER-   207: DEMODULATION SECTION-   208: P/S SECTION-   209: ASSIGNMENT INFORMATION ACQUISITION SECTION-   210: TRANSMISSION RF SECTION USER    FIG. 2, 6, 7-   FROM FFT SECTION 204-   2051: BLOCK EXTRACTION SECTION-   2052: PILOT EXTRACTION SECTION-   2053: SNR ESTIMATION SECTION-   2054: SNR AVERAGE CALCULATION SECTION-   2055: SNR DISPERSION CALCULATION SECTION-   2056: CHANNEL ESTIMATION VALUE CALCULATION SECTION-   2057: CHANNEL DISPERSION CALCULATION SECTION-   2058: PILOT DISPERSION CALCULATION SECTION TO TRANSMISSION RF    SECTION 210    FIG. 3, 8-   SUBCARRIER NUMBER-   CASE-   SNR DISPERSION-   NORMALIZED SNR ERROR    FIG. 4-   1/SNR DISPERSION-   AVERAGE SNR-   NO TRANSMISSION

1. A wireless transmission apparatus that performs adaptive modulationwith a multicarrier signal formed with a plurality of blocks, each blockincluding a plurality of subcarrier signals, the wireless transmissionapparatus comprising: a selection section that selects modulationschemes of the plurality of blocks on a per block basis; and amodulation section that modulates the plurality of subcarrier signals inthe plurality of blocks using the modulation schemes selected on a perblock basis, wherein the selection section selects the modulationschemes on a per block basis based on an average channel quality of allblocks and channel quality of each block representing propagation pathcharacteristics of each block.
 2. The wireless transmission apparatusaccording to claim 1, wherein the average channel quality comprises anaverage of SNRs.
 3. A wireless reception apparatus communicating withthe wireless transmission apparatus according to claim 1, the wirelessreception apparatus comprising: a reception section that receives themulticarrier signal; and a reporting section that reports the averagechannel quality of all blocks and the channel quality of each blockrepresenting propagation path characteristics of each block.
 4. Amodulation scheme selection method used in a wireless communicationsystem where adaptive modulation is performed with a multicarrier signalformed with a plurality of blocks, each block including a plurality ofsubcarrier signals, the method comprising: a selection step of selectingmodulation schemes of the plurality of blocks on a per block basis; anda modulation step of modulating the plurality of subcarrier signals inthe plurality of blocks using the modulation schemes selected on a perblock basis, wherein, in the selection step, the modulation schemes isselected on a per block basis based on an average channel quality of allblocks and channel quality of each block representing propagation pathcharacteristics of each block.